1. Field of the Invention
The present invention relates generally to the data compression-decompression field.
2. Description of the Prior Art
The advent of powerful data compression-decompression algorithms and the advantages resulting therefrom in terms of transmission line occupancy rate have involved the CCITT (International Telegraph and Telephone Consultative Committee) in defining, during the year 1989, a data compression recommendation for data circuit-terminating equipment (DCE) employing error correction procedures. This recommendation, designated as Recommendation V.42bis, Geneva 1989, is limited to the asynchronous, or more exactly, arhythmic transmission mode.
According to this recommendation, a data terminal equipment DTE, or terminal, is connected to a transmission network via a data circuit-terminating equipment DCE, or modem. The data terminal equipment DTE transmits characters in asynchronous mode to the data circuit-terminating equipment DCE. The characters are compressed as and when received by a V.42 bis modem, then grouped and packed to form a frame with safe link. This frame is then transmitted in the transmission network.
Thus the V.42bis recommendation does not consider the case of transmission from the terminal equipment in synchronous mode. In the case of such a transmission, the data produced by the terminal equipment are no longer arhythmic characters, but more sophisticated frames.
Thus, prior to this invention there remained the need for data circuit-terminating equipment enabling data compression for terminal equipment in synchronous mode.